1. Field of the Invention
The present invention relates generally to electric vehicles (EVs) and hybrid electric vehicles (HEVs), and specifically to using an on-board navigation system for energy management.
2. Discussion of the Prior Art
The need to reduce fossil fuel consumption and emissions in automobiles and other vehicles predominately powered by internal combustion engines (ICEs) is well known. Vehicles powered by electric motors attempt to address these needs. Another alternative solution is to combine a smaller ICE with electric motors into one vehicle. Such vehicles combine the advantages of an ICE vehicle and an electric vehicle and are typically called hybrid electric vehicles (HEVs). See generally, U.S. Pat. No. 5,343,970 to Severinsky.
The HEV is described in a variety of configurations. Many HEV patents disclose systems where an operator is required to select between electric and internal combustion operation. In other configurations, the electric motor drives one set of wheels and the ICE drives a different set.
Other, more useful, configurations have developed. For example, a series hybrid electric vehicle (SHEV) configuration is a vehicle with an engine (most typically an ICE) connected to an electric motor called a generator. The generator, in turn, provides electricity to a battery and another motor, called a traction motor. In the SHEV, the traction motor is the sole source of wheel torque. There is no mechanical connection between the engine and the drive wheels. A parallel hybrid electrical vehicle (PHEV) configuration has an engine (most typically an ICE) and an electric motor that work together in varying degrees to provide the necessary wheel torque to drive the vehicle. Additionally, in the PHEV configuration, the motor can be used as a generator to charge the battery from the power produced by the ICE.
A parallel/series hybrid electric vehicle (PSHEV) has characteristics of both PHEV and SHEV configurations and is sometimes referred to as a xe2x80x9cpowersplitxe2x80x9d configuration. In one of several types of PSHEV configurations, the ICE is mechanically coupled to two electric motors in a planetary gear-set transaxle. A first electric motor, the generator, is connected to a sun gear. The ICE is connected to a carrier. A second electric motor, a traction motor, is connected to a ring (output) gear via additional gearing in a transaxle. Engine torque can power the generator to charge the battery. The generator can also contribute to the necessary wheel (output shaft) torque if the system has a one-way clutch. The traction motor is used to contribute wheel torque and to recover braking energy to charge the battery. In this configuration, the generator can selectively provide a reaction torque that may be used to control engine speed. In fact, the engine, generator motor and traction motor can provide a continuous variable transmission (CVT) effect. Further, the PSHEV presents an opportunity to better control engine idle speed over conventional vehicles by using the generator to control engine speed.
The desirability of electric motor powered vehicles (EVs) and combining an ICE with electric motors (HEVs) is clear. Fuel consumption and emissions can be reduced with no appreciable loss of vehicle performance or drive-ability. The HEV allows the use of smaller engines, regenerative braking, electric boost, and even operating the vehicle with the engine shutdown. Nevertheless, new ways must be developed to optimize EVs and HEVs potential benefits.
One way to optimize electric powered vehicles is efficient energy management. A successful energy management strategy must balance fuel economy, maintain critical vehicle function capacity, (i.e., assuring sufficient stored electrical energy), while always meeting driver demand for power. For example, the control system needs to maintain the battery state-of-charge (SOC) at a level to meet performance requirements while allowing it to accept any upcoming regenerative braking energy. Without knowledge of the possible upcoming power requirements or regenerative braking events, the control system has to conservatively predict and compromise battery SOC.
A possible solution to assist a vehicle system controller (VSC) to predict and adapt to upcoming vehicle power requirements and regenerative braking is the use of a navigational system that uses a global positioning system (GPS) and a digital map database. While this idea is known in the prior art, such systems do not utilize the full potential of navigation system derived information for energy management and efficiency.
U.S. Pat. No. 5,892,346 to Moroto et al. generates an electric power schedule for an EV or an HEV based on a starting point and a destination. A navigation system acts as an arbitrator for feasible routes based on distance traveled en route to the destination compared to the distance capacity of the vehicle. This invention uses the navigation system as a pre-trip planning tool that would, for example, reject the longest proposed routes. See also, U.S. Pat. Nos. 5,832,396 and 5,778,326 to Moroto et al. Similarly, U.S. Pat. No. 5,927,415 to Ibaraki et al., allows the use of a navigation system in advance as a pre-trip planning tool for an HEV to assure power demands are met.
U.S. Pat. No. 6,202,024 to Yokoyama et al. discloses the use of a navigational system on a continuous basis to provide a xe2x80x9cbest drive route.xe2x80x9d The invention is not concerned with energy management, nor is it concerned with electric vehicles. For example, it can use a bi-directional navigation system to develop, among other things, a database of road conditions in any given area based on receipt of the same road condition data from a plurality of vehicles in the same area. If several vehicles are reporting use of anti-lock braking systems or air bag deployment, the xe2x80x9cbest drive routexe2x80x9d would be diverted from that area.
A vehicle control system for an EV or HEV that can tightly integrate a navigational system, such as a GPS with a map database, for continuous vehicle energy management is needed.
Accordingly, the present invention integrates an on-board navigation system to provide energy management for an electric vehicle (EV) and a hybrid electric vehicle (HEV).
The present invention provides a system and method to manage energy in a vehicle with an electric traction motor comprising, a powertrain with at least one motor and an engine, a battery connected to the motor, a vehicle system controller (VSC) connected to the vehicle powertrain, a device connected to the VSC to continuously locate a present vehicle location and infer expectations of driver demand, and a strategy to continuously accommodate fuel economy, driver demand for power and function of the battery.
The system can be configured to include as part of its present vehicle location data on road patterns, geography with date and time, altitude changes, speed limits, identification of intersections with traffic control features such as stop signs and traffic lights, driving patterns of a vehicle driver, and weather.
The strategy can be configured to use discrete control laws, fuzzy logic, or neural networks.
Driver demand or expectation can be based on a driver communicating an intended drive route, or through the use of a search of maps for the locale of the vehicle.
Other objects of the present invention will become more apparent to persons having ordinary skill in the art to which the present invention pertains from the following description taken in conjunction with the accompanying figures.